13157721 has 14 divisors (see below), whose sum is σ = 19728650. Its totient is φ = 8771328.

The previous prime is 13157701. The next prime is 13157723. The reversal of 13157721 is 12775131.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 12702096 + 455625 = 3564^2 + 675^2 .

It is not a de Polignac number, because 13157721 - 2⁵ = 13157689 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (13157723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 13 ways as a sum of consecutive naturals, for example, 8296 + ... + 9753.

Almost surely, 2^13157721 is an apocalyptic number.

It is an amenable number.

13157721 is a deficient number, since it is larger than the sum of its proper divisors (6570929).

13157721 is an frugal number, since it uses more digits than its factorization.

13157721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18067 (or 18052 counting only the distinct ones).

The product of its digits is 1470, while the sum is 27.

The square root of 13157721 is about 3627.3573025000. The cubic root of 13157721 is about 236.0805587760.

The spelling of 13157721 in words is "thirteen million, one hundred fifty-seven thousand, seven hundred twenty-one".